Landfills that have been expanded multiple times over a period of decades are limited in future volume expansions by previously designed leachate collection systems. Extending leachate cleanout and access pipes vertically from the base of a landfill as waste is placed in the landfill has proven difficult. This is because waste that is placed in a landfill decomposes at different rates throughout the landfill and is not stable from a geotechnical perspective. In non-landfill applications above ground, a vertical pipe is often stabilized by a strong foundation and compacted backfill and is designed to withstand horizontal loads. However, designing a strong foundation for a vertical riser is not practical in a landfill due to technical and regulatory constraints.
Landfills, often divided into separate cells, are currently designed with a clay and geosynthetic base liner and a liquid collection system at the base of each cell. The liner materials are not permitted to be penetrated in order to prevent liquid from leaking out of the landfill. Environmental regulations require that landfills maintain less than a one-foot depth of liquid head on the liner and that the collection pipes be limited in length for cleaning purposes, typically less than 2000 feet in length. With limited success, landfill owners and engineers have attempted to bring collection pipes to the surface with different manhole configurations. However, these manholes have typically failed over time due to the large differential settlements seen in landfills. This differential settlement results in horizontal and vertical forces causing pipes or manholes to tilt or shear. Once a manhole in a waste mass starts to lean, a downward vertical force acts on the manhole with little upward resistance because the waste cannot support the weight of the manhole.
Most landfills currently do not overlay waste over leachate collection pipe access points (leachate side slope risers on the perimeter of the landfill) due to concerns over environmental compliance issues caused by the possibility of a failed leachate collection system. Not being able to expand the size (length and/or width) of the landfill reduces the value of the site and requires new areas to be developed as landfills.
What is needed, therefore, is an apparatus in a landfill wherein waste of the landfill can be overlaid above one or more leachate collection pipe access points so that the length and/or width of the landfill can be extended, reducing the need for opening new landfills.